1. Field of the Invention
The present invention relates generally to a tissue separation cannula used for forming an elongated cavity in tissue planes particularly along the course of a small blood vessel, and more specifically relates to a cannula having an endoscope for continuously visualizing the blunt dissection site through a tissue separating member which is transparent and has a tapered shape.
2. Description of Background Art
Present methods for the formation of an elongated cavity involve the use of blunt probes that are pushed through body tissue to accomplish the tissue dissection. The force exerted by the passage of mechanical probes may lead to blood vessel avulsion and trauma to tissue and internal organs.
The problem becomes acute when dissecting and harvesting blood vessels having a small diameter of about 3 to 8 mm. The techniques which are used for dissection of larger blood vessels such as the aorta are not applicable since the aorta is located in the retroperitoneum bounded by the peritoneum on one side and the psoas muscle on the other side. An everting balloon placed in the infrarenal space located just below the kidney will track easily down the length of the aorta along a natural cleavage plane when inflated.
An everting type of balloon encounters difficulties when dissecting tissue adjacent a smaller-diameter vessel. This is due to the presence of less distinct planes that exist between small diameter blood vessels and the tissue that surrounds these vessels. as compared with the aorta and the tissue that surrounds the aorta. For example, if an everting balloon is placed adjacent to the saphenous vein in the leg, it usually skews dissection upon inflation rather than track along the vein. This is due to the amorphous nature of the fat and connective tissue that surrounds the saphenous vein.
Everting balloon catheters are known which are used for arterial dilation. (See. for example, U.S. Pat. No. 4,479,497 (Fogarty et al., Oct. 30, 1984) and U.S. Pat. No. 4,863,440 (Chin. Sep. 5, 1989)).
Double lumen everting balloon catheters, such as those disclosed in the Fogarty et al. ""497 and the Chin ""440 patents, have a through-lumen that slidably receives an endoscope. However, an endoscope used in conjunction with those disclosed catheters is unable to monitor the dissection process, since the endoscope lies within the central lumen proximal to the everting balloon. As the balloon everts from the catheter, the internal inflation pressure squeezes the walls of the balloon and closes off the distal viewing channel. Also, the area that requires monitoring during balloon dissection is located at the advancing front of the everting balloon. This area corresponds to the balloon/tissue interface that is subject to forces which cause tissue separation. Thus an endoscope in the central lumen of existing double-lumen. everting balloon catheters is unable to view the area of tissue separation, since a double layer of balloon membrane lies between the endoscope and the tissue and blocks the endoscopic line of sight This double layer obscures and distorts the viewing area of tissue separation.
Endoscopes have been disclosed for use in optical trocars such as in U.S. Pat. No. 5,385,572 (Nobles et al., Jan. 31, 1995) and EP 0 642 764 A1 (Sauer et al., published Mar. 15, 1995) and in harvesting blood vessels such as in U.S. Pat. No. 5,373,840 (Knighton, Dec. 20, 1994). The Nobles et al. ""572 patent and the Sauer et al. ""764 application disclose the use of sharp-tipped, metal cutting elements which extend outwardly from an endoscope positioned in the trocar. Control of the dissection is difficult because visualization of the vessel is obscured by the collapse of the tissue planes into the area between the cutting element and the endoscope. Furthermore, the risk of side vessel avulsion or trauma to the vessel is greatly increased by the orientation of the outwardly extending cutting elements.
The endoscope disclosed in Knighton ""840 has a lateral dimension of a size sufficient to accommodate the blood vessel being harvested and at least one tool for use in harvesting the blood harvested. However, the failure of the endoscope to enlarge a cavity adjacent the blood vessel obscures viewing of the dissection area and manipulation of the vessel therein. The position of the viewing image relative to the tissue dissection area could obscure the identification of side vessels leading to an increased risk of vessel avulsion. Since the vessel is retrieved through the center of the endoscope, all side vessels must be severed for the endoscope to advance and the length of the vessel thus retrieved is limited substantially by the length of the body of the endoscope.
The present invention provides a cannula for bluntly dissecting an elongated cavity in tissue particularly along the course of a vessel. The cannula includes a tubular body having proximal closed end and distal blunt end and at least one lumen extending the length of the body. The cannula also includes an endoscope having a lighted, viewing end disposed in the lumen near the distal end of the body, and includes a transparent, tissue separating member substantially covering the distal end of the body. The tissue separating member has a blunt tip disposed towards the distal end of the body.
A method is also disclosed for bluntly dissecting an elongated cavity particularly along the course of a vessel using a cannula. The method includes the steps of: bluntly dissecting an initial cavity; separating the tissue by advancing the cannula along the cavity with continuous, visual observation; repeating the prior step of separating the tissue at least until the cavity is sufficiently elongated to advance a balloon therein; and successively inflating and deflating a balloon within the cavity to enlarge the cavity along the course of the vessel. The method further may include removing the cannula, then maintaining the elongated cavity using insufflated gas through a balloon cannula that seals the incision against gas leakage, or using a structural balloon, or a mechanical structural support.
In another embodiment of the present invention, the method includes the steps of bluntly dissecting an initial cavity; sealing and inflating the cavity; and separating the tissue along the cavity assisted by continuous, visual observation while under inflation until the cavity is sufficiently elongated.
The isolated vessel such as the saphenous vein, may be harvested and removed for use as a coronary artery or vascular graft, or may be left in place as an in-situ femoropopliteal or femoral-distal graft. The side branches of the vein are ligated, clipped, or occluded in both applications. In the case of an in-situ graft, the valves in the vein are disrupted by means of a valvulotome.